Theoretical Studies of the Structural, Mechanical and Raman Spectroscopic Properties of Uranyl-Containing Minerals

Abstract

The incipient use of theoretical methods in the research of geomaterials reveals the great power of such methodology in the determination of the mineral properties. These methods provide a safe, accurate and cheap manner of obtaining these properties. Uranium-containing minerals are highly radiotoxic, and their experimental studies demand a careful handling of the samples used. However, theoretical methods are free of such inconveniences and may be used in the complete characterization of this type of minerals. Theoretical methods are not only a complement to the use of other experimental techniques but also a powerful predictive tool. The structural, mechanical and Raman spectroscopic properties of uranyl-containing materials, including rutherfordine soddyite, schoepite and uranophane-α, were studied by means of theoretical solid-state methods based on density functional theory using plane waves and pseudopotentials. A new norm-conserving relativistic pseudopotential for uranium atom developed in recent works was employed. These minerals are among the most important secondary phases arising from corrosion of spent nuclear fuel under the final geological disposal conditions. The computed crystal structures of these materials as well as the corresponding and X-ray powder patterns were found to be in excellent agreement with the experimental information. Therefore, the optimized structures of these minerals were employed to study the mechanical properties and stability of these minerals. These properties were obtained using the finite deformation technique. All these minerals were found to be mechanically stable since the corresponding Born stability conditions were satisfied. A large amount of relevant mechanical data were reported including bulk, Young and Shear moduli, Poisson ratios, ductility and hardness indices, anisotropy measures as well as longitudinal and transversal wave velocities. The large volume expansion and mechanical stress resulting from the corrosion of spent nuclear fuel during storage emphasize the great relevance of the mechanical information of the waste components. Finally, the computation of vibrational properties of these minerals is studied. The computed Raman spectra of these materials were found to be in good agreement with their experimental

Thermodynamic properties of the uranyl carbonate minerals roubaultite, fontanite, widenmannite, grimselite, čejkaite and bayleyite

“…[49][50] The knowledge of the crystal structures of uranyl-containing minerals is interesting itself for the investigation of the paragenetic sequence of minerals arising from the oxidative dissolution processes of uraninite in uranium ore deposits 8,10,15,19,[51][52] and spent nuclear fuel (SNF) in NWRs, 8,,11,20.40-45 and for the evaluation of the incorporation of fission products and actinides in the corresponding structures. [53][54][55][56] However, the availability of the full crystal structures of uranyl containing minerals is also relevant because opens the possibility of the safe and efficient computation of their vibrational spectra [47][48][57][58][59][60][61][62][63][64][65][66][67][68] and physicochemical properties 46,48, employing the first principles solidstate methodology. The knowledge of the optimized structures of the uranyl carbonate minerals rutherfordine, bayleyite, roubaultite, fontanite, widenmannite, grimselite and čejkaite [46][47][48] was exploited for the theoretical determination of their mechanical properties.…”

Thermodynamic, Raman Spectroscopic, and UV–Visible Optical Characterization of the Deltic, Squaric, and Croconic Cyclic Oxocarbon Acids

“…The computed crystal structures are displayed in Figure . For the calculations of the Raman spectra, the linear response density functional perturbation theory (DFPT), − implemented in the CASTEP code, a module of Materials Studio package, was used in the same way as in previous works. ,,− The theoretical solid-state methodology used in this paper has been employed not only for organic and metal-organic materials ,,,− but also for a large series of uranyl-containing compounds such as oxides, oxyhydroxides, − peroxides, carbonates, ,, and silicates. , In all of these cases, the results were very satisfactory.…”

The crystal structures and mechanical properties of the uranyl carbonate minerals roubaultite, fontanite, sharpite, widenmannite, grimselite and čejkaite

“…[94][95][96][97][98][99][100][101][102] Information provided by these computational treatments has been shown to be extremely rich in recent years, providing fresh new methods for spectroscopic assignment and interpretation of the results of experimental studies. 94,[97][98][99][100][101][102][113][114][115][116][117][121][122]126 The achievement of this information is impossible from the use of experimental techniques and the theoretical methodology has allowed the safe and accurate prediction of highly relevant material properties of these minerals, such as their mechanical properties and thermodynamic functions, [94][95][96][97][98][99][100][101][102][107][108]110,113,[116][117][118][119][120][121][122][123][124]…”